Does a junior ADU (JADU) need a Title 24 energy report?

Usually yes, but the scope is often small, and what applies depends on whether you're converting space that's already conditioned (an alteration) or conditioning space that wasn't before (an addition). JADUs that are additions also get one notable break: they don't have to meet the whole-dwelling ventilation airflow requirement.

What counts as a JADU for the Energy Code

The 2025 Energy Code defines a junior accessory dwelling unit as a dwelling unit of no more than 500 square feet, contained entirely within a newly constructed or existing single-family building. It has a kitchen, a separate entrance and an interior entry to the main living area, and it may have its own bathroom or share one with the main home.

Three common JADU scenarios

• Converting an existing bedroom or conditioned area: this is an alteration. Only the components you add or change, such as a new mini-split, water heater, lighting, kitchen exhaust or insulation, must meet the alteration rules.
• Converting unconditioned space inside the home: newly conditioned space must meet the requirements for an addition under Section 150.2(a). That brings in envelope, HVAC, lighting and water heating requirements for the new area.
• A JADU designed into a brand-new house: it's part of the newly constructed building and is covered by the new-construction compliance for the whole home.

The ventilation exception

Section 150.2(a)1C says JADUs that are additions to an existing building don't have to provide the whole-dwelling ventilation airflow in Section 150.0(o). They still must meet the local exhaust rules: a kitchen exhaust or range hood, and bathroom exhaust if the JADU has its own bathroom. For JADUs created through alterations, the CEC notes that ventilation requirements may come from the California Mechanical Code, which may in turn point back to Section 150.0(o). The CEC refers questions on that to the Department of Housing and Community Development (HCD).

What a JADU usually does not trigger

• No solar PV: the Energy Code's PV requirement is for newly constructed buildings, and the code says PV is not required for additions.
• Small-space options: additions of 500 square feet or less may use an electric water heater with point-of-use distribution instead of a heat pump water heater, if the reference appendix piping limits are met.

When a report may not be needed

If you make no change to any regulated system or the envelope, there may be little or nothing to document. Most JADUs add a kitchen, lighting and often heating or cooling, though, and those changes are regulated. Your building department decides what documentation it needs.

What this means for your MEP plans and Title 24 report

We identify whether your JADU is an alteration or an addition, then document only the measures that apply. The mechanical, electrical and plumbing sheets then match the CF1R. See Title 24 reports, the ADU Title 24 guide, and California ADU requirements.

Sources: energy.ca.gov, energy.ca.gov, energy.ca.gov.